The present invention relates to a process for preparing phthalocyanine pigments with improved dispersion characteristics. More specifically, it relates to preparing dry pigment compositions in the absence of an inorganic salt grinding step.
The introduction of phthalocyanine pigments in 1935 set new standards of excellence in the pigments consuming industries. They are characterized by their excellent light fastness, intensity, bleed and chemical resistance, extreme stability and exceptionally high tinting strength. phthalocyanine pigments are restricted to the blue and green regions of the spectrum. Because of their excellent color values, working properties and low cost in addition to durability, the phthalocyanine blue and green pigments are used extensively.
The two processes most generally employed for producing copper phthalocyanine pigments are (1) heating phthalic anhydride, urea, a copper salt and a catalyst with or without a reaction medium such as chloronaphthalene or trichlorobenzene to 180.degree. to 200.degree. C. and (2) heating phthalonitrile and a copper salt with or without a reaction medium or solid diluent. The product that results is generally a copper phthalocyanine blue pigment of about 65 to 70 percent purity.
The product produced by these processes is a crude phthalocyanine pigment. As used herein, the term "crude pigment" defines a colorant that has a much larger particle size than does its pigment grade; for example, the particle size of the crude grade of phthalocyanine is generally about 40 to 50 microns or larger whereas the particle size of its pigmentary grade is generally about 0.01 to 1 micron.
There are many known methods for conditioning crude pigments, such as dry grinding the crude phthalocyanine in the presence of an inorganic salt grinding aid such as an alkali metal halide, carbonate, sulfate or phosphate.
In the preparation of inks, paints, colored plastics, and the like, it is essential that the pigment be uniformly dispersed in the vehicle. There are many techniques for improving dispersibility of pigments such as adding the pigment in the form of a fine powder. However, solvent type inks such as nitrocellulose present a particularly difficult problem due to the high viscosity of the base ink. Poor viscosity hinders dispersion and the ultimate color characteristics of the finished inks. Accordingly, it is the purpose of the instant invention to prepare a phthalocyanine pigment, and particularly phthalocyanine blue pigment, which exhibits excellent flow in solvent type inks, particularly nitrocellulose.
______________________________________ Patents of Interest Country Patent No. Issued Inventor(s) Assignee ______________________________________ British 2,042,576 9/24/80 BASF U.S. 3,598,625 8/10/71 Buckwalter Cities Service et al U.S. 4,371,643 2/1/83 Thomas Cyanamid U.S. 4,448,607 5/15/84 Johnson et al Sun Chemical ______________________________________
British No. 2,042,576--teaches the premilling process employed as step IA of this invention as set forth below.
U.S. Pat. No. 3,598,625--discloses preconditioning a phthalocyanine blue crude pigment in a ball mill followed by salt grinding in the presence of an organic liquid which organic liquid may be glycol or glycol ethers. Ethylene glycol and diethylene glycol are specifically mentioned.
U.S. Pat. No. 4,448,607--discloses milling crude phthalocyanine with a phthalimidomethyl phthalocyanine derivative and in the absence of any milling or grinding aid such as salt.
U.S. Pat. No. 4,371,643--discloses dry grinding copper phthalocyanine pigments in the presence of hydroxylic solvents such as water, ethylene glycol, monobutylethers of ethylene glycol and a polar polymer and, in the absence of salt.